This invention deals with hard, curable, clear and pigmented release coatings for cookware and bakeware. For years, it was a common method in the commercial baking art to utilize natural fats, greases and vegetable oils for coating cookware to obtain release of the cooked goods from the cookware, but in the early part of the decade beginning with 1960, the commercial cooking industry, especially the baking industry, was introduced to polyorganosiloxanes as a means of obtaining release of foods and baked goods from the cookware. Originally, the application of such organopolysiloxane release materials consisted of substituting the fluid organopolysiloxanes for the natural release agents in anticipation that the organopolysiloxanes would be more durable in use and thus require less down time in order to treat the cookware units.
The release coating technology moved quickly as various curable, thus more durable, organopolysiloxanes were introduced to the industry. These more advanced release coatings usually consisted of hydroxy-containing fluids, which were usually linear polydimethylsiloxanes, dissolved in higher viscosity phenylmethylpolysiloxanes or, such linear materials were combined with solvent-based or solventless organopolysiloxane resins and cured onto certain substrates, by the application of heat, to cause condensation reactions. Other, more modern, release coatings utilizing siloxanes involved the combination of a linear, hydroxylated, diorganopolysiloxane, a phenylmethylpolysiloxane and an organopolysiloxane block copolymer which is heat cured unto the substrate. Such a coating is described in U.S. Pat. No. 3,308,079, issued Mar. 7, 1967 and cures through condensation reactions of the silanols present in the siloxane components.
A similar release coating material is described in U.S. Pat. No. 3,308,080, issued Mar. 7, 1967, except that the phenylmethylpolysiloxane does not form part of the composition.
In U.S. Pat. No. 3,925,276, issued on Dec. 9, 1975, there is described a process for preparing a silanol-containing organopolysiloxane resin which is useful as a release resin. This type of resin is described as giving good release to sugar-containing baked goods. This type of resin, with a fairly specific ratio of alkyl and aryl siloxanes, cures by heat curing through condensation reactions.
U.S. Pat. No. 4,204,021 deals with a composite layer concept for release purposes wherein a first coating is applied to a porous ceramic layer and impregnates the porous ceramic layer. The top layer is a release layer and the patent describes organopolysiloxanes as part of a group of known release coatings wherein there is present in the organopolysiloxane, an unsaturated radical on silicon, which when combined with a photosensitizer, can be cured by exposure to a free radical light source.
British Patent No. 1,448,985, issued Sept. 8, 1976, describes pigmented release coatings that are obtained by a two coat composite method, in which, the bottom coat is a cured pigmented coating and the top coat is a hard, transparent release coating. The hard, transparent release coating is generally described as a silicone resin that gives release. No additional information is given about the release coating which would enable one to ascertain its composition or cure mechanisms.
Finally, there is disclosed in U.S. Pat. No. 3,419,514, issued Dec. 31, 1968, an "air-dried" version of an organopolysiloxane-based release coating. The coating contains a phenylmethylpolysiloxane having a hydroxyl content of at least 3 percent by weight, a phenyl to silicon ratio of at least 0.3 and a total phenyl and methyl to silicon ratio of from 1.2 to 1.7; RO(R'CHCH.sub.2 O ).sub.2 H; methylpolysiloxane fluid having at least 2% by weight of silicon-bonded hydroxyl groups and ##STR1## These materials cure at room temperature in a very short period of time by reaction of the acetoxysilane with moisture in the air and subsequent condensation reactions under the influence of catalysts.
Since the instant invention can be described in-part as an "air-dried" release coating, the '514 reference is, in the applicants' opinion, the closest prior art. None of the other references are considered by the applicants to anticipate or make obvious the instant invention and further, and even though the '514 patent is considered pertinent prior art, it differs from the instant invention in at least the following manner: most importantly, the crosslinking means of the instant invention consists of the inclusion of CH.sub.3 Si(OCH.sub.3).sub.3 in the composition. This alkoxy silane, upon hydrolysis, liberates non-corrosive methanol which is removed quickly during the cure reaction whereas the crosslinking means of the '514 reference liberates acetic acid during the cure reaction. This acetic acid is both corrosive to metal substrates and is extremely difficult to remove during the cure reaction.
Further, the essential base siloxane of the '514 reference is a phenylmethylpolysiloxane whereas the essential base siloxane of the instant invention is a copolymer of four specific alkyl and/or aryl-containing siloxane units. Component (c) of the reference material is similar in composition to component (C) of the instant invention but the instant composition does not contain the organic polyether, component (b) of the '514 reference. Therefore, even though the two inventions have a common ingredient, i.e., component (c) in each case, and even though they both claim to have air-dry properties, it is quite obvious that the comparison stops there and the material of the instant invention is not the same as the material of the '514 reference.